Delayed action explosive munition



y 18, 1954 L. M. PRINCE, JR., ETAL 2,678,603

DELAYED ACTION EXPLOSIVE MUNITION Filed Aug. 15, 1944 2 Sheets-Sheet 1LEON N. PRINCE) L/R. Log/1s G, W/LLKE y 8, 1954 M. PRINCE, JR., ETAL2,678,603

DELAYED ACTION EXPLOSIVE MUNITION Filed Aug. 15, 1944 2 Sheets-Sheet?Louis 6, W/LL E- 1 501v PRINCE; L/R.

Patented May 18, 1954 DELAYED ACTION EXPLOSIVE MUNITION Leon M. Prince,Jr., New York, N. Y., and Louis G. Willke, United States Army, EdgewoodArsenal, Md., assignors to the United States of America as representedby the Secretary of War Application August 15, 1944, Serial No. 549,602

(Granted under Title 35, U. S. Code (1.952),

sec. 266) 3 Claims.

The invention described herein may be manufactured and used by or forthe Government, for governmental purposes without the payment to us ofany royalty thereon.

This invention relates to munitions and particularly to bombs having adelayed action burster or fragmentation unit.

Munitions with which this invention is particularly concerned areincendiary aircraft bombs of the intensive type, e. g., thermit filledbombs for causing disruption of military importance. This type of bombis intended to cause a conflagration by a concentrated high temperatureburning as a unit until consumed.

Explosive incendiary bombs were developed to discourage fire fightingaction. At first, explosive incendiaries were made by incorporating asmall burster charge of black powder into the noses of the bombs to havean explosion occur when the incendiary charges burned down. These bombsfailed to give more than a small explosion, just a puff, and resultedonly in harass ing or frightening fire fighters. Later, attempts weremade to use high explosives as burster charges, but difficulties wereencountered in obtaining satisfactory tactical results, since withoutproper delay action the high explosive, in functioning too soon afterimpact, scatters the incendiary filling before incendiary action occurs,reveals the location of the incendiaries, and fails to act as a delayedrestraint against fire fighting efforts. Similarly, if the explosion isconsistently delayed to the end of the burning of the incendiary, thesurprise factor is reduced. A common difficulty in designing explosiveincendiaries has been in using high explosive charge in standardizedincendiary bombs with positive but variable delayed detonation afterimpact on target surfaces of various degrees of hardness, e. g., on theground or on concrete.

To obtain improved explosive incendiary bombs which avoid previousdifficulties, this invention has amongother objects those of providingincendiary bombs with high explosive bursters without necessitating anysubstantial changes in the appearance, weight or ballistics of thebombs. It is concerned with providing the bombs with a fragmentationburster having a high explosive charge of lethal proportions incombination with a detonating means which is portioning and constructingthe burster unit in such a manner that the high explosive issatisfactorily protected against premature ignition or decomposition byhigh temperature heat generated in the bomb before such heat effects thefunctioning of the detonator so that the explosion is made to occurthrough the functioning of the detonator. It has the additional objectof providing an explosive bomb constructed so as not to interfere withthe assembling, loading, handling, clustering, aiming, and functioningof the bombs.

The foregoing and further objects of the invention will be understoodfrom the following detailed description in conjunction with theaccompanying drawings and claims. I

Without being limited thereto, the invention is described with referenceto several practical embodiments illustrated in the accompanyingdrawing, in which;

Figure l is a longitudinal sectional view of one type of incendiary bombwith a delayed action explosive unit.

Fig. 2 is an elevational view of the tail end of the bomb on a largerscale;

Fig. 3 is a cross sectional view taken on line 33 of Fig. l on a largerscale;

Fig. 4 is an elevational view of the nose end of the bomb shown in Fig.1 on a larger scale;

Fig. 5 is a longitudinal sectional view of a nose end portion of anothertype of explosive incendiary bomb;

Fig. 6 is a longitudinal sectional view of a nose end portion of a 3rdtype of an explosive incendiary bomb;

Fig. 7 is a longitudinal sectional view of a 4th type of delayed actionexplosive incendiary bomb;

Fig. 8 is a cross-sectional view of a truncated cone delay element whichmay be alternately used in place of a disc or other shape of delayelement interposed between a thermit filling and the top end of a livedetonator in a burster.

' It will be understood from the following dcscription that thisinvention is concerned with the utilization of various shapes, sizes andkinds of metal delay elements for influencing the time required fortransmission of heat from a burning incendiary agent in a bomb insuiiicient intensity to activate a suitable heat-sensitive detonatorand, in turn, a high explosive burster charge in predetermined timeranges.

change in construction and appearance;

(2) Positive functioning of the explosive charge under all climaticconditions and with different kinds of impact;

(3) Variable delay in explosion from a few secondsto about 10 minutesafter impact; and

(4) Capability of producing casualties and damage over a substantialarea.

In general, the assembly of the burster, detonator, and delay elementsis'torbexlocated munition where heat can be conducted at a suitable ratefrom a burning chargein the inunition through the delay element to thedetonator. With explosive incendiary bombs-of .tlie thermit-type, thepractice is to place this assembly at the nose end of the bombs. "Itiszdesirable to fill the bomb casing with a thermit-type incendiaryagent, commonly known as thermit, pressed in from the top of thecasing'andito irn sert the burster and detonator from the nose andfollowing the thermit loading.

Referring particularly to Fig. 'l of the draw- .ings,.an explosive,incendiary bomb formingone embodiment of this invention comprises a body.5, made of cast magnesium or magnesium alloy, hexagonally shaped,.and'filled with a thermit chargefi. A 'cast iron or steel nose I,mortised intothe nose (lower) end of body 5 serves as a .bursteroase andalso serves to make the-bomb plummet with suitable'velooity in anuprightpo- -sition-when dropped from aircraft.

A first fire charge 8 is loaded through the tail (upper) end of body'5.The first fire charge 8 is pressed into a truncated conicalprojection 9.tofill 'a-corresponding-shaped recess at the-end of thermit charge :6.A small depression In is .formed :in-the center of the exposed'surfaceof :the first firecharge 8 toaidignitionthereof.

The first fire charge 8 is formulated to be readily ignited by astandard'type of primer cap 11, spaced therefrom and held in a primercap :holder [2 of steel or "aluminum which seats agaigist the shoulder!3 formed in,the:boclycasting;

The primer cap is adapted-to be fired by afiring pin I 4 disposedina-firingpin holder 15. The firing pin 14 may be-made of aluminum orsteel :and includes "a weight portion H5. The firing piniweight portion[6 has a'projection l8 of re- :duced diameter adapted to set within aturnedin flange 19 of the-firing pin'holder'l5. The'firing pin I4 isnormally retained :in the position shown'by means TOfELSClGW .2 and across-shaped bracememberi l. The cross-shaped member'z'l is made ofbrass or other deformablematerials, :so that 'upon a predeterminedimpact of the "bombythe crossed strips'of this-member willyfold up andpermit the firing pin I4 to slide toward the primer cap l l.

The -firing pin "assembly is held in place by screws-22. A safety pin.23 is provided with "a :spring'24 fitting therearound to tend toforce'the safety :pin 23 in a-zwithdrawn or armed position. This type ofbomb'is adapted to beloadedinto :clusterssothat anumber of bombs, forexample,

:50 or more, 'fit against one another to press the 7 safety pins 23,into-an unarmedposition, wherein the safetypins 23-pushed under thefiring pins 44 prevent accidental movement of the firing pins towardthe-primer caps l I.

Lhexagonally shaped tail 215 is attached to the tail (upper) end of thebody and is held in place Iby'the screws 22. The tail 25 stabilizes thedownward flight of the bomb. Vent .holes .noropenings 2Sare'formedin:thebodynasting 5 between the primer cap holder .12 :andtheifirst Crv from the burning charge.

plugs 2'1.

"tratediin Fig.;1,'which has been standardized, has

fire charge 8. The outer ends of the holes 26 are counterbored so as toreceive plugs or stoppers 2?, which may be made of rubber, fibre boardor metal cups, which are blown out by gases evolved Inxorder .to makethe bomb waterproof, the outer surfaces of the plugs .2! are coated witha waterproof cement or lacquer, preferably, the inner surfaces of theholes 26 are-also lacquered before the insertion of the One practicalform of the bomb illusatotal weight of about four lbs. and an overalllength .of about 21% inches. The magnesium alloy casting 5 has a weightof about 1 lb. 4 oz.,

ra lengthof: aboutll inches and for the greater part of its length, hasa thickness of about 1%". A suitable thermit mixture for forming the.corexihargefi :has the following composition in percentage by weight:

Per cent Aluminum,. granular .15.? to 16.3 .Iron oxide .scaleor .ironore 43.5 to 144:5 Aluminum, grained -8.8-to .92 Barium nitrate 28.6 to29.4 Sulfur 1.9 ,to 2.1

The weight of the chargefiin a bomb weighingabout 4 lbs. is about 265grams. The therlnate charge 6 is preferablyloadedinto the body 5 in fourapproximately equal increments .under a dead loadpressure of 6,000 to7,000 lbs. using a ram shaped to formatruncated conica1 \depressioncorresponding to the shape of .the truncated projection 9 of thefirstfirecharge-fl.

The firstfire charge ,8 for a-ZGSgram-thermit charge should weigh about:19 to.21 grams and may be pressed on top the charge v6 underadeadload'of 6000 to 7000 lbs. 'using'a .ram shaped .to form aroundeddepression ID. A suitable first fire charge composition comprises 25%mag- .nesiumrpowdenand barium chromate.

Next, referring more particularly-to the nose end assembly shown in Fig.1, the steel or iron nose cup 1 is mortised into the nose end of thebody ;5, and has integral parts/28 and 29 of .reduced-cross-section:at'its inner end. The nose cup 1 base relatively large -.ho1low chamber30 for containing a suitablelhighexplosive. .At its frontend-opening,the nose cup .l-is threadedto receive'a closure plugalprovided'with-drill holes 32 for receivingaspanner wrench intightening the pluginto position. A fibrous or felt pad .3-3

.isplaced adjacent the plug 3| in closing thaexplosion chamber after ithas been loaded with high explosive and witha detonator .tube 13-4inserted into a central bore 35 through the-reduced cross sectionextension :29. -A metal or plastic disc =36 may be placed in theexplosion chamber "38 ;-at the base of :the detonator tube 34 .to offerresistance :to the movement -.of the detonator tube when the bombissubjected to impact. -A delay element disc .3-1 .-is interposed at.theendof the .nose cupextension .29 between the thermate'filling'fiandtheopen inner end of the-,detonator tube 134. The materiaLshapeandsize of this disc 3'l is.-a factor in determiningrthe delay period fortransmission :of heat from the burningpart of the bomb to the detonatorior initiating detonation of the high explosion in chamber .30.

Ina bomb having substantially the construction illustrated in Fig. 1asteel disc approximately 0.960" in diameter and 0.0.6 sthick .may

be dropped .into the body from .the tail .end prior to loading .of :thebody with nthermit .and :first dire charge. Following the loading withthe nose cup 1 in position, the detonator 34 may then be insertedthrough the open end with plug 3| removed until the open end of thedetonator tube contacts with the underside of the steel disc 31.

With a suitable detonator tube thus in place, and a suitable highexplosive, such as tetranitromethylaniline, filling the explosionchamber 30, the nose cup is closed by screwing in the threaded plug 3i.

In a bombing operation, when a cluster of the bombs is released fromaircraft, bands which hold the bombs in the clusters are broken so as topermit the individual bombs to fall separately in a pattern toward thetarget. As the bombs separate from one another, the safety pins 23 whichwere pressed inwardly in the cluster are released to the position shownin Fig. 3 so as to arm the bombs. Upon impact of the nose end of a bomb,the inertia movement of the weight portion !8 of the firing pin !4 actsto deform the retaining cross shaped member 2i so as to allow the firingpin I4 to strike the primer cap I I. The primer cap II flashes into thedepression III of the first fire charge 8, thereby igniting this charge.The gases produced by the combustion of the ignited first fire charge 8develop sufficient pressure to blow out the vent hole plug 21, thusleaving a passage for escape of combustion gases evolved by the burninincendiary charge so as to prevent explosion of the incendiary unitbefore the delayed explosive unit functions.

The first fire charge 8 burns at a temperature sufficiently high toignite the thermate charge 6, which in turn ignites the adjacent body 5of the bomb where an intense incendiary action is obtained. A portion ofthe heat tends to flow through the bomb body toward the nose end wherethe burster unit is located. The intensity of the heat which reaches theburster unit depends on the proximity of the burning portion of theincendiary charge 6, the burning advancing gradually toward the nose endof the bomb.

When bombs assembled as described were tested by static firing, delaysfrom about 1 minute up to 12 minutes and longer, from the instant thethermate began to burn until the explosion, were obtained. On droppingthese bombs from a plane at 1,000 feet and 4,300 feet onto concrete, theaverage delays were even longer on account of the tendency of thedetonator to be set back a short distance from the steel disc 31 and,accordingly, the variable delay range was somewhat increased but Withoutmisfires of the explosive,

Statically fired, the average delay was about 1 minute 45 seconds, andon dropping onto concrete the average delay was approximately 2 minutes30 seconds measured from the instant of impact till the explosion. Arough approximation of the percentages of explosions in varied delayranges were: 10% in l to 2 minutes; 50% in 2 to 3 minutes; in 3 to 4minutes; 10% in i to 5 minutes; and 5% in 5 to 12 minutes.

Thus, it was determined that a very satisfactory variation in delay isobtainable with substantially no failures in explosion.

Investigation shows that a number of readily available high explosivescould be used satisfactorily in the nose cup. Tetryl was generallysatisfactory. Trinitrotoluene, particularly in pellet form, Tetrytol andHexalite gave good results even though they were at first suspected ofbeing too sensitive to thermal decomposition for such a use and thechamber may be charged with til O the jacket 38.

one or more of these explosives instead of tetryl. It is thus indicatedthat construction with suitable delay elements and a proper detonatorserves to preserve the high explosive until the detonation action isinitiated in the detonator through delayed heat transmission thereto,even after the incendiary agent in the bomb has been consumed.

The detonator tube 34, in general, comprises a slow burning train ofnon-explosive powder leading to a primer and a booster explosiveenclosed in a flexible metallic jacket. A detonator of this type has analuminum or copper gildingmetal jacket 38, 0.274 inch 0. D., open at thetop where the delay train is exposed and closed at the bottom. The delaytrain powder 39 com- ;prising preferably a readily reducible metaloxide, and a readily oxidizable element is compressed in a lead tubing40 staked tightly within At the open end of the jacket 38, the delaypowder is extruded flush with the-top of the jacket. A delay powdercomprising barium peroxide and silicon ignites at approximately 300 C.and undergoes practically gasless autocombustion, at a rate ofapproximately 5 seconds per inch, thus burning from end to end in about1 to 3 seconds. This delay train terminates in an ignition charge M of a-30 mixture of lead ortho-cresol and potassium chlorate,diazo-dinitrophenol, or the like. Three rains of this charge 4i pressedat 200 lbs.,'ignites at about 270 C. The ignition charge is pressedagainst a primer charge 42 comprising lead azide, or the like, disposednext to a bottom booster charge 43 made up of 14 grains of tetryl,preferably phelgmatized.

Following the principles set forth, the detonator may have variedingredients. This type of detonator occupies a very small space. It issatisfactorily stable against shock and against changes by variedclimatic conditions. The thin flexible metal container or jacket issubject to some deformation on impact of the bomb, but this deformationdoes not interfere with the functioning of the detonator but rathertends to increase the delay in the action of the detonator. 1

In the type of bomb having a nose as illustrated in Fig. 5, thedetonator tube I34 inserted in the neck or extension 29 of the steelnose 1 has a flanged top 44 which serves to hold the detonator tube I34in position against the metallic delay element I31. In place of a steeldisc, a magnesium disc about 0.064" thick may act as the partitioningdelay element I31. The magnesium disc acts to protect the detonatorwhile the thermate is being loaded. When the thermate nearly burns downto this magnesium disc, the magnesium disc burns quickly and promptlyinitiates the burning of the delay powder train in the detonator I34.The desirability of this action lies in the fact that this bomb may bemistaken as a long delay bomb and those who attempt to extinguish thebomb before a delayed explosion will be injured or killed. In actualtests, of the explosions occurred in 60 to '70 seconds after impact, andthe remaining 25% before a minutes.

In the type of bomb nose assembly illustrated in Fig. 6, the metallicdelay element 231 is cast integral with the bomb body 5. The detonatortube 234 is inserted into a hole drilled into the partitioning member231 which is cast integral with the body 5, but a 4;" thickness ofmagnesium separates the top of the detonator from amen i? am zthermate;sand :this ithiekness -;of magnesium #acts in the ssame-iway as 0.j06"-steeLdisc. iltmrewants iflame :frem reaching the :detonator randeservesto delaythe flow-of heatto-the detonator. fSevcral-perforateddiscs :46 of high meltin 'point rplastic,;such asphenol-iormaldehydezresin, may the ad sposed ,to collar the detonator:tube 34 ato "serve as an insulation and guide for furtherproztection=-yof the detonator and the highexplosive iin-zthis-typeoi construction.

:By; forming the integral vdela-y partition mem- :ber-i331ain theshapeof a truncated cone,asishown in SEE. -7, tl-iede1ay peri0d may beshortened moreauniformly, for when the thermit surroundsingtheconegbegins to burn-the cone is readily ignited and-thereuponheat isquickly transferred to the detonator tuhe234. However, a separateconical disc element43l' (see Figr8) maybe used ,',-instead of "anintegral partition member should {fiffShOItQi jdelay be desired. Bombswith -theconi qcal delay element produced 85% of the explos-ions :35 to60 seconds after impactandtheaemaining 15% of explosions weredistributedfrom el'atoi3zminute'intervals after impact.

-'I -heoretical principles "which -may "be considered as involved in thefunctioning of the heat itra-nsmit-ting delay elements are:

v('1) {The delayaelementsserving to protect the 'detonator from theflame and heat generated:by stheburning thermate for aperiod afterimpact are capable vof conducting heat of sufllcienteinrtensit-y "toinitiate "the action of the 'detonator hefore :heat conducted to thenose cup can-affect itheihigh explosive therein;

(12) The delay in heat transmission to there plosive in the nosecupand-to'thephargeinthe detonator is a function ofathe distancethat.:;the :heat must travel to reach these charges.

.zA ;-f avora-ble characteristic of --the detonato r giS ;that;itpermits the high explosive'charge itOEbe icept 1 intact until fired bydetonation. -In=the -;delayed :action detonating means described, ethere:are .no Zmoving parts and its elements are :not {fractured under; the:strains and shocks imposed :apon impact 20f the high :velocity bomb.The ntypes'of delay -Vmeans used eeliminate theineed of any pyrotechnicdelays which are suscelltible to -jdamaging ,by the shock incurred, and"which xmustbe provided with elongated connecting-links H'avhichvreguire excessive ;spacetand :work :in as- :sembling. The. delayelements-zus,edrintthepres- -ent invention are simple andddeally suitedfor large (scale production with ravlninimum whence ior difficulties.

L'ItiiS r130 be=understood -that-theinvention:is;not

3 etc gbeilimited iby .theiorms or embodiments ede- ;-.SO1' -ib.d nor;by;'any theory of: mechanismof their operation, but that modificationscome :within the spirit and scope thereof.

1. ,A bombincluding a=casing, a recessednose ,portiommortised into thefront end-10f ithe Leasing, said nose portion containing a ,highiexplorsive-cha-rge: in its front end portion and "an F6101).-

gated detonator tube to the rearzofsaidqcharge, :saidcasing containingaslidabiy mounted firing min; a primer cap-holder spaced apart ,fromandin frontof saidfiring pin, afirstfiring charge spaced apart "from "andin 'front of said ,firing :primer capholder, athermit charge in front-ofssaid firing :charge, said .first firing charge, -,and --.said:.therrnitcharge being highlycompacted together after being loaded in thecasingysaid jdetonator tube :beingopen "at its rear send por"tion-and'havingan ignition charge in .its front vend -portion anda-delay powder-train forignit- :m said ignition charge. Y

2. The-bombof-cl-aim 17in which the rear .end -p0rtion-of-thefirstifiring charge iszrecessedpand its :front end portion-is rammedinto a a recess in therea-rendportion of said thermit-charge.

:3. The bomb of claim 1 in which thefiring charge consistsofan:admixture of magnesium :poWder-and -barium chromateand the thermitcharge consists essentially ofa highly compacted gadmixturejof sulphur,grained aluminum,;granular aluminum, barium vnitrate and -a compound'ofxironrandnxygen.

References :oGited in thefileof this patent UNITED STATES PATEN-TS{Number .Name Date 1329.8;222 Kane V .Mar. "25,, 19.19 ,,1 ,36l','2i86,Ratrick V. r Dec. 2,;1920 1 ,43 6,24;8 Hammond" N0v.'21, 192.2 I2.',O93,35 3 "Geitmann Sept. 14,193? 42,316,656 rWa1ker F Apr. 13, 19.4312,318,994 Helmhold r e May '11, 11943 FOREIGN :PATENTS "Number CountryDate 1,250,271 Great Britain 0017.21, 1926 669,007 Germany Dec. '14,{1938 66,996 Norway Oct. 25,1943

OTHER REFERENCES :Popula-rfiSciencejMarch 1943, page 115. (Copy

